README.md

FastAPI Demo

This demo runs the same FastAPI service on three event loops:

• stdlib asyncio
• uvloop
• rsloop

When started with --event-loop rsloop, the demo explicitly enables rsloop fast streams before importing the loop implementation.

Prerequisites

If the Rust extension is not already built locally:

uv run --with maturin maturin develop --release

The demo itself uses temporary dependencies from uv, so nothing needs to be added to the project package metadata.

Run

From the repository root:

uv run --with fastapi --with uvicorn python demo/fastapi_service.py --event-loop asyncio --no-access-log
uv run --with fastapi --with uvicorn --with uvloop python demo/fastapi_service.py --event-loop uvloop --no-access-log
uv run --with fastapi --with uvicorn python demo/fastapi_service.py --event-loop rsloop --no-access-log

Service entrypoint: demo/fastapi_service.py

std-async is also accepted as an alias for stdlib asyncio:

uv run --with fastapi --with uvicorn --with uvloop python demo/fastapi_service.py --event-loop std-async

Endpoints

• / returns the selected loop and basic service info
• /health returns a simple readiness payload
• /sleep?delay=0.05 exercises timer scheduling
• /fanout?tasks=500&delay=0 exercises concurrent task scheduling
• /stream-loopback?roundtrips=100&payload_size=256 exercises asyncio.start_server() and asyncio.open_connection(), which use rsloop fast streams in rsloop mode

Example:

curl http://127.0.0.1:8000/
curl "http://127.0.0.1:8000/fanout?tasks=1000&delay=0"
curl "http://127.0.0.1:8000/stream-loopback?roundtrips=200&payload_size=512"